The following relates to reflective flat panel display systems and, in particular, to improving color characteristics of display images rendered by such systems.
Flat panel systems include controllable display cells, such as liquid crystal display cells, that impart image information onto light transmitted from a light source. The light passes through the display cell to an analyzer (e.g., a polarizer) that resolves the light into a display image that is provided at a display output.
Transmissive display systems include a high-intensity backlight that functions as the light source and cooperates with the display cells to provide a reasonably high brightness display. Such display systems are employed a variety of electronic devices including, for example, portable personal computers and other computing devices. Such electronic devices in portable operation rely upon a battery power source, and the current draw of a high-intensity backlight imposes a severe limit on the duration of battery-powered portable operation.
Reflective display systems, including high-resolution, multi-color reflective display systems, utilize ambient light to generate display images. No backlight is used. Ambient light received at the viewing surface of a reflective display system passes through a display cell to a reflector, and is reflected back through the display cell to the viewer with an imparted display image. Electronic devices such as portable computers with reflective display systems avoid the battery-powered operating time limitations characteristic of devices with transmissive display systems.
Without a high-intensity backlight, a reflective display system will typically be designed to maximize the amount of ambient light that can be used to maximize the display brightness. In a multi-color display with color filters for generating multiple primary color components (e.g., red, green, and blue), the spectral ranges of light transmitted by each color filter are typically maximized. This can result in significant overlaps in the spectral ranges transmitted by the nominal color filters for the different primary color components.
While improving display brightness, such overlaps in color filter spectral ranges can decrease the accuracy with which colors are rendered by a reflective display system. In particular, overlapping spectral ranges means that pure color components cannot be rendered because of the spectral overlap or xe2x80x9ccross-talkxe2x80x9d between the color filters. Nevertheless, the improvements in image brightness provided by wide spectrum, overlapping color filters has made such calorimetric inaccuracies an acceptable characteristic of reflective display systems.
Accordingly, an improvement in multi-color reflective display systems includes a controllable display cell and multiple non-sequential, typically adjacent, color filters that transmit generally different color components with spectral overlaps between them. The improvement includes a color filter cross-talk compensator that receives image data that corresponds to a display image to be rendered. The color filter cross-talk compensator generates cross-talk compensated color component drive signals that are delivered to the display cell. The cross-talk compensated color component drive signals compensate for the overlapping color components transmitted by the nominal color filters for the generally different color components.
In one implementation, the cross-talk compensator includes an illumination source selector for selecting the ambient light as being one of multiple predefined ambient illumination sources. The cross-talk compensator compensates for the overlapping color components transmitted by the color filters differently according to the ambient illumination source that is selected. For example, the ambient illumination sources may include daylight or interior fluorescent lighting.
Another aspect of the improvement is a multi-color reflective display color filter cross-talk compensation method. In one implementation for displays with nominal red, green and blue color filters, the method includes determining for each color filter a transmittance at each of multiple selected light wavelengths throughout the spectrum. From these transmittances, the relative amounts of red, green and blue light transmitted from each color filter are determined and are normalized with respect to the transmittance of the nominal colors of the filters. Color filter cross-talk compensation factors are determined from the normalized relative color components transmitted from the color filters, and image data signals are applied to the reflective display in accordance with the color filter cross-talk compensation factors.
Additional objects and advantages of the present invention will be apparent from the detailed description of the preferred embodiment thereof, which proceeds with reference to the accompanying drawings.